The present invention relates to an improvement in elastic stoppers for thermoplastic containers, and in particular, for plastic stoppers around which thermoplastic container neck portions can be molded.
Elastic stoppers for containers are, of course, known. Typically, such stoppers comprise a cap having an upper portion which is disc-shaped and a lower portion in the form of a downwardly depending skirt which extends into the neck of the container. These stoppers are used in glass containers in conjunction with an aluminum overcap, or the like, to retain the stopper within the container.
However, when such stoppers are used in conjunction with thermoplastic containers that are molded thereabout by conventional blow molding techniques, or otherwise, it has been found that a satisfactory seal between the container and the stopper is not always formed. Using such techniques the stopper is positioned within the mold cavity the parison is extruded about the stopper, and the mold is closed thereabout. The parison is then blown to form the container and is squeezed about the stopper in the neck portion. However, owing to the compression of the stopper during the molding process the stopper is deformed and bulges outwardly a slight amount and the parison necessarily conforms to the bulged-out contour of the stopper during the molding process. When the mold halves are removed, the pressure on the resilient stopper is relieved and the stopper substantially returns to its original shape. This causes portions of the stopper to pull away from the wall of the container neck molded thereabout and can result in a defective seal about the stopper.
The above-described sealing problem is especially severe in molded, thermoplastic containers having a very small neck portion and, consequently, require a very small stopper. The problem is particularly acute with stoppers having an outside diameter of about one-half inch or less, and in particular, with stoppers having an outside diameter of less than about 0.4 inch.
It would be desirable to provide a small stopper of the type and size discussed above with a configuration which would permit a container to be molded about the stopper in place to form an effective seal between the stopper and the container.